1. Field of the Invention
The invention relates to method and apparatus for previewing the results of a data structure allocation in an information handling system and, more particularly, to a method and apparatus for previewing the results of an allocation of a cache or list structure in such an information handling system.
2. Description of the Related Art
The S/390 Parallel Sysplex configuration is a cluster of interconnected processing nodes with attachments to shared storage devices, network controllers, and core cluster technology components, consisting of coupling facilities, coupling support facilities, and sysplex timers. A coupling facility (CF) enables high-performance read/write sharing of data by applications running on each node of the cluster through global locking and cache coherency management mechanisms. It also provides cluster-wide queuing mechanisms for workload distribution and message passing between nodes.
The coupling facility is described in the following patents and publications, incorporated herein by reference:
"In a Multiprocessing System Having a Coupling Facility, Communicating Messages between the Processors and the Coupling Facility in Either a Synchronous Operation or an Asynchronous Operation", by D. A. Elko et al., Ser. No. 08/420,893, filed Apr. 11, 1995, now U.S. Pat. No. 5,561,809; PA1 "Sysplex Shared Data Coherency Method And Means," by D. A. Elko et al., Ser. No. 07/860,805, filed Mar. 30, 1992, now U.S. Pat. No. 5,537,574; PA1 "Method And Apparatus For Distributed Locking Of Shared Data, Employing A Central Coupling Facility," by D. A. Elko et al., Ser. No. 07/860,808, filed Mar. 30, 1992, now U.S. Pat. No. 5,339,427; PA1 "Command Quiesce Function," by D. A. Elko et al., Ser. No. 07/860,330, filed Mar. 30, 1992, now U.S. Pat. No. 5,339,405; PA1 "Software Cache Management Of A Shared Electronic Store In A Sysplex," by D. A. Elko et al., Ser. No. 07/860,807, filed Mar. 30, 1992, now U.S. Pat. No. 5,457,793; PA1 "Multiple Processor System Having Software For Selecting "Shared Cache Entries Of An Associated Castout Class For Transfer To A DASD With One I/O Operation," by D. A. Elko et al, Ser. No. 07/860,806, filed Mar. 30, 1992, now U.S. Pat. No. 5,493,668; PA1 "Command Execution System For Using First And Second Commands To Reserve And Store Second Command Related Status Information In Memory Portion Respectively," by D. A. Elko et al., Ser. No. 07/860,378, filed Mar. 30, 1992, now U.S. Pat. No. 5,392,397; PA1 "Integrity Of Data Objects Used To Maintain State Information For Shared Data At A Local Complex," by D. A. Elko et al, Ser. No. 07/860,800, filed Mar. 30, 1992, now U.S. Pat. No. 5,331,673; PA1 "Management Of Data Objects Used To Maintain State Information For Shared Data At A Local Complex," by J. A. Frey et al, Ser. No. 07/860,797, filed Mar. 30, 1992, now U.S. Pat. No. 5,388,266; PA1 "Clearing Data Objects Used To Maintain State Information For Shared Data At A Local Complex When At Least One Message Path To The Local Complex Cannot Be Recovered," by J. A. Frey et al., Ser. No. 07/860,647, filed Mar. 30, 1992, now U.S. Pat. No. 5,394,542; PA1 "Coupling Facility For Receiving Commands From Plurality Of Hosts For Activating Selected Connection Paths To I/O Devices And Maintaining Status Thereof," by D. A. Elko et al., Ser. No. 08/324,447, filed Oct. 18, 1994, now U.S. Pat. No. 5,463,736; PA1 "Data Processing System And Method For Providing Notification In A Central Processor Of State Changes For Shared Data Structure On External Storage," by J. A. Frey et al., Ser. No. 07/860,809, filed Mar. 30, 1992, now U.S. Pat. No. 5,390,328; PA1 "Method And Apparatus For Performing Conditional Operations On Externally Shared Data," by J. A. Frey et al., Ser. No. 08/383,532, filed Feb. 1, 1995, now U.S. Pat. No. 5,742,830; PA1 "Apparatus And Method For List Management In A Coupled Data Processing System," by J. A. Frey et al., Ser. No. 07/860,633, filed Mar. 30, 1992, now U.S. Pat. No. 5,410,695; PA1 "Interdicting I/O And Messaging Operations In A Multi-System Complex," by D. A. Elko et al., Ser. No. 07/860,489, filed Mar. 30, 1992, now U.S. Pat. No. 5,394,554; PA1 "Method And Apparatus For Coupling Data Processing Systems," by D. A. Elko et al., Ser. No. 07/860,803, filed Mar. 30, 1992, now U.S. Pat. No. 5,317,739; PA1 "Authorization Method For Conditional Command Execution," by D. A. Elko et al., Ser. No. 08/408,446, filed Mar. 22, 1995, now U.S. Pat. No. 5,450,590; PA1 "Dynamically Assigning a Dump Space in a Shared Data Facility to Receive Dumping Information to be Captured," by D. A. Elko et al., Ser. No. 08/471,895, filed Jun. 7, 1995, now U.S. Pat. No. 5,664,155; PA1 "Method And System For Capturing and Controlling Access To Information In A Coupling Facility," by D. E. Neuhard et al., Ser. No. 08/146,647, filed Nov. 1, 1993, now U.S. Pat. No. 5,630,050; PA1 "Method and Apparatus for Expansion, Contraction, and Reapportionment of Structured External Storage Structures", by D. J. Dahlen et al., Ser. No. 08/304,458, filed Sep. 12, 1994, now U.S. Pat. No. 5,581,737; PA1 "Method of Managing Resources in One or More Coupling Facilities Coupled to One or More Operating Systems in One or More Central Programming Complexes Using a Policy," by R. A. Allen et al., Ser. No. 08/607,053, filed Feb. 26, 1996, now U.S. Pat. No. 5,634,072; PA1 "Method and System for Managing Data and Users of Data in a Data Processing System," by R. A. Allen, Ser. No. 08/146,727, filed Nov. 1, 1993, now U.S. Pat. No. 5,465,359; PA1 "Method and System for Reconfiguring a Storage Structure Within a Structure Processing Facility," by R. A. Allen et al., Ser. No. 08/544,941, filed Oct. 18, 1995, now U.S. Pat. No. 5,515,499; PA1 "Method for Coordinating Executing Programs in a Data Processing System," by R. A. Allen et al., Ser. No. 08/439,269, filed May 9, 1995, now U.S. Pat. No. 5,604,863; PA1 "Coherence Controls for Store-Multiple Shared Data Coordinated by Cache Directory Entries in a Shared Electronic Storage," by K. S. Carpenter et al., Ser. No. 08/148,707, filed Nov. 8, 1993, now U.S. Pat. No. 5,544,345; and PA1 J. M. Nick et al., "S/390 cluster technology: Parallel Sysplex", IBM Systems Journal, vol. 36, no. 2, 1997, pages 172-201.
Currently, users of the Coupling Facility must be provided with formulas that enable them to determine what target structure size to use in order to obtain a desired number of entries and elements in a list or cache structure. Additional formulas are provided to enable them to compute the number of entries and elements that will result when a structure is allocated with a given structure size.
The formulas that are currently provided have two problems: (1) they yield results that are only approximate, and (2) the formulas have to be updated as changes are made to the CF architecture and implementation. The approximate nature of the results yielded by the formulas has been a source of trouble, since some users prefer a bias in one direction while other users prefer a bias in the other direction. In addition to being time-consuming, updates to the formulas can cause trouble when a user fails to obtain the version of the formulas appropriate to the level of the CF he is working with.